Three rings 2-hydroxypyridine liquid crystalline compounds have been prepared and fully characterized. The mesomorphic behavior of the prepared compounds has been investigated in terms of differential scanning calorimetry (DSC) and polarized optical microscopy (POM). Moreover, a comparative study between the prepared compounds and previously reported analogs has been discussed in terms of the orientation and position of the mesogenic core, in addition to the direction of the terminal alkyl chains. Furthermore, a detailed computational approach has been studied to illustrate the effect of geometrical and dimensional parameters on the type of the enhanced texture and the mesomorphic range and stability. The results of the DFT study revealed that the orientation of the mesogen could affect the mesomorphic behavior and this has been attributed in terms of the degree of the polarizability of the linking groups. This result has been confirmed by calculation of the net dipole moment and the molecular electrostatic potential that show how the mesogen orientation and position could impact the molecular charge separation. Finally, the effect of the pyridyl group has been also investigated in terms of the calculated aromaticity index and the π-π stacking.

In the present work, two series of Coumarin based Schiff base-esters mesogenic compounds have been synthesised. The first series (KSC-(6–18)) comprises of Schiff base of alkoxy 4-formylbenzoate and 7-alkoxy-3-aminocoumarin with symmetric variation of alkoxy chain at the both ends that have been designed and prepared. In the second series (KC-(6–18)), octyloxy chain on coumarin end was kept constant with variation at the other end. All new mesogens were characterised using various analytical techniques including FTIR, NMR, elemental and mass spectral analysis. The textures of the mesomorphic properties were investigated using polarising optical microscope (POM) and differential scanning calorimetry (DSC). In series (KSC-(6–18)), on varying the alkyl chain length at the both end of molecules systematically, an enantiotropic smectic A phase behaviour was observed for compounds with chain lengths (n = 6, 8, 10, 12). Compounds of the (KSC-(6–18)) series with (n = 14, 16, 18) were non-mesogenic. In the (KC-(6–18)) series with octyloxy chain at coumarin end, an enantiotropic smectic A mesophase was observed for all compounds (n = 6-18). The DFT calculations have been carried out and the theoretical study was discussed in terms of dipole moment, molecular electrostatic potentials, frontier molecular orbitals and geometrical structure along with aspect ratio. GRAPHICAL ABSTRACT